Using antibodies as cell type specific markers, we propose to study the development of surface antigens on neurons and glia and probe for their involvement in cell function or cell-cell interactions in the nervous system. We shall investigate Thy-1 glycoprotein antigen as a surface marker for neurons of the central and peripheral nervous system using immunofluorescent techniques and dissociated cell cultures. We shall determine when embryonic dorsal root ganglion neurons first develop the antigen in vivo, and study its expression in vitro. Also to be studied are sympathetic ganglion cells grown under different culture conditions, and cerebellar cell cultures, in which two different Thy-1 positive neuronal-looking cells develop. The neuronal identity of a known large Thy-1 positive cell shall be investigated using autoradiographic and ultrastructural methods. We shall determine whether chromaffin cells in cultures of fetal rat adrenals express the Thy-1 antigen. Exocytosis in these cultures will be studied and whether vesicle fusion is accompanied by a movement of glycoproteins on the surface tested. Using a neuronal tumor cell line, we shall investigate the relationship of differentiation to tetanus toxin binding, and test whether the appearance of toxin binding is accompanied by the synthesis of Gdlb or GT1 gangliosides, which are putative toxin receptors. Using these cells we shall test for an effect of tetanus toxin on transmitter release. We shall continue to characterize a Schwann cell antigen, Ran-1, and to use this antigen to follow the cell interactions of peripheral Schwann cells and cerebellar neuronal cells in mixed cell cultures. In general, every effort will be made to extend the use of cell specific immunological markers beyond problems of cell identification to study questions of neuronal and glial cell function in health and disease.